The use of electrolytic cells in the commercial production of chemicals by electrolysis is old in the art.
Particularly is this true in the production of chlorine, caustic, and hydrogen by the electrolysis of aqueous solutions of sodium chloride. Electrolytic cells for this purpose generally have a multiplicity of cathodes and anodes generally arrayed in a alternate, parallel fashion within the cell. Diaphragm Chlor-Alkali electrolytic cells nearly always have the diaphragm disposed between each anode and cathode. Most often the diaphragm is deposited on the external surface of the cathodes. The cathodes are usually shaped so as to form a hollow chamber within the working faces of the cathodes. The working faces are foraminous surfaces to allow passage of the fluid electrolyte from the anode compartments through the diaphragms and through the foraminous cathode working faces into the interior of the cathodes. In most chlorine cells the anodes have long been made of graphite usually having the shape of solid rectangular prisms.
During the assembly of such cell as described above, much damage is often done to the diaphragms by their being scraped by the anodes as the anodes are slid past the diaphragms into their operational position interleaved between the cathodes. To minimize this damage these graphite anodes have to be designed with a smaller thickness than is desired for optimum cell operating efficiency. However, insofar as electrical energy power lost is concerned during cell operation, the thickness of these graphite anodes should be capable of being enlarged in order to minimize the distance between the opposing anode and cathode working faces; i.e., to reduce the electrical resistance path. This distance is referred to as the anode-cathode gap. Thus in the use of anodes whose thickness could not be varied, such as with the graphite anodes, there has existed a trade-off in the thickness design of the anodes, this trade-off being occasioned by the competing considerations of having a thicker anode to reduce the anode cathode gap to effect electrical power savings against the consideration of having a more narrow anode to have a wide anode-cathode gap to reduce the risk of diaphragm damage during cell assembly.
One anode assembly has recently been designed to overcome this anode-cathode gap width trade-off. It is an anode assembly which can be caused to have a large anode-cathode gap during cell assembly by reducing the overall thickness of this anode assembly, but yet one having the capability of reducing the anode-cathode gap during cell operation by expanding the overall thickness of the anode. This expandable anode assembly is disclosed in U.S. Pat. No. 3,674,676 (Fogelman July 4, 1972). It was made possible by the breakthrough in chlor-alkali anode design of replacing the solid graphite electrodes with the so-called dimensionally stable anodes.
These dimensionally stable anodes are thin anode sheets of metals such as titanium, tungsten and tantalum. These dimensionally stable anodes have a much higher coefficient of electrical conductivity than do the graphite anodes. At the same time they withstand the corrosive attack of the hostile environment surrounding the anodes in chlorine cells; i.e., an aqueous mixture of brine, hydrochloric acid, and chlorine gas as does the graphite.
In serving as an improved replacement for the graphite anodes, the above identified expandable anode assemblies utilize several parts. Further, all of these parts must be electrically connected. The electrical conductivity of each anode part requires each of the several parts to be made from the same or similar, expensive, electrically conducting (but non-corrosive) metals as are the anode working faces. Furthermore, when dealing with the special metal there is required a high degree of skill as well as special equipment to make the several necessary welded connections. This increases manufacturing costs to prohibitive amounts when manufacturing such anodes for commercial use. This difficulty in assembly, the relatively large number of parts required, and the expense of materials is significantly reduced by the present invention.